Electronic counting scale

ABSTRACT

There is disclosed an electronic counting scale provided with means for calculating a maximum addable number of items to be added to an already counted known number of items with an error being eliminated from the counted number of a total items including the added items, said means calculating the maximum addable number on the basis of the standard variation of an average weight estimated from the samples taken from the entire population of the items to be counted.

FIELD OF THE INVENTION

The present invention relates to an electronic counting scale, namely anapparatus for counting the number of items from their weight, and moreparticularly to an electronic counting scale which adopts a method thatunknown number of items are successively added to a known number ofitems first loaded on the scale.

BACKGROUND OF THE INVENTION

There has been disclosed in a Japanese Patent Publication No. 57-44128an item counting system wherein a known number of items is first weighedto obtain a provisional average weight per item and, after any unknownnumber of items is added, the total weight is measured and then dividedby the provisional average weight. The quotient of the division isrounded to the nearest integer to give the total number of itemsincluding the number of the added items. The total number thus obtainedis used also to revise and increase the accuracy of the provisionalaverage weight given previously. The total weight is divided by thetotal number to give a revised provisional average weight per item. Thissystem, however, has a disadvantage that, if the number of the addeditems is too many, the quotient derived from the total weight divided bythe provisional average weight may include an error which amounts tonearly an integer, resulting in giving an error of unity or larger tothe total number obtained. In such a case any "rounding" operation onthe quotient becomes nonsense as well as an investigation of theaccuracy of the provisional average weight. Therefore, once an error isintroduced in the total number, any of the thereafter followingaverage-revising processes can not eliminate the counting error.

SUMMARY OF THE INVENTION

Accordingly, it is a principal object of the present invention toprovide an electronic counting scale which calculates in advance toaddition of items the number of items addable without generating anerror, whereby a scale operator can add and count as many items aspossible at one time within a limit free from a counting error. Anotherobject of the present invention is to provide an electronic countingscale which informs a scale operator of an excessive addition of itemsby eliminating the numerical figures displayed on the number display orby displaying a specific mark, if the scale is loaded additively withitems in excess of a maximum addable number. A further object of thepresent invention is to provide an electronic counting scale whichcalculates an error-free addable number of items according to a table ora function prepared beforehand on the basis of known information aboutthe statistical weight distribution of the items to be counted.

The apparatus based on the present invention comprises a weighing trayto be loaded with items whose number is to be counted, a weightmeasuring means for measuring a gravitational force acting on said itemsloaded on said weighing tray and for outputting a digital weight valuecorresponding to said gravitational force, a central processing unitwhich includes an arithmetic organ for processing said digital weightvalue according to a predetermined program, a memory for storing variouscalculating formulae, various calculated values and said predeterminedprogram, a number displaying means for displaying the number of saiditems calculated by said arithmetic organ, and an informing means forinforming whether the number of items added on said weighing tray isequal to or exceeds the number calculated according to a predeterminedform of calculation.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing the electric circuitry used in anembodiment of the present invention.

FIG. 2 is a flow chart showing the program of the embodiment.

FIG. 3 is a flow chart showing the program of another embodiment of thepresent invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

FIG. 1 is a block diagram showing the electric circuitry used in anembodiment of the present invention. A weight detector 1, comprising aload cell or a weight-and-electromagnetic force equilibrating unit,outputs at predetermined time intervals a digital weight datacorresponding to the weight loaded on a weighing tray 11. A control unit2 consists of a microcomputer which comprises an input port 21 forreceiving measured data and set values, an output port 22 for outputtingmeasured results, a RAM 23 for storing measured and calculated values, aROM 24 for storing a program and arithmetic formulae, a driver 25 for adisplay unit 3, a key matrix 26 to which key signals are to be inputfrom a key board 5, a CPU 27 to control the whole according to abelow-described program. The RAM 23 contains data registers devised soas to accept and retain the successively input newer data by pushing outand disposing the previously retained older data. The display unit 3displays the contents of the display registers A and B provided in theCPU 27. An informing means 4 informs a scale operator whether the numberof added items coincides with or exceeds a calculated maximum addablenumber of items. The "maximum addable number" here means the maximumnumber of items addable without generating a counting error. Theinforming method is, for instance, by means of eliminating the displayedfigures, displaying a specific mark or lighting a separately equippedinforming lamp. The key board 5 contains not only figure keys but also areleasing key 52 for releasing the informing performance of theinforming means 4 and a key 53 for inputting a coefficient of variation.

FIG. 2 is a flow chart showing the contents of the program stored in theROM 24. In the first place several samples each of which consists of thesame number n of items are weighed to estimate the weight-scattering inthe population. The number p of the samples is stored beforehand in thememory according to the program. The weight W_(i) of each sample isdivided by the number n of sample-constituent items to give the averageweight

    m.sub.i =W.sub.i /n, (i=1, 2, . . . , p)                   (1)

of n items, and thus obtained p average weight values are stored in thememory at Step 1. Each time the weighing-and-averaging process iscarried out on the p samples, the values n and W_(i) are transferred tothe registers A and B, respectively. After all of the p samples areweighed and averaged, the operational process is directed to Step 2. AtStep 2 the average weight X₀ of the total n×p items (or the average ofm_(i)), the standard deviation σ and the coefficient of variation C_(v)are calculated according to the following equations: ##EQU1## Step 2 isthen followed by Step 3, where the total number of the items loaded onthe scale at this stage of process is calculated as an "initial" totalnumber N₀ according to the equation given below, (though the initialtotal number is, of course, known to be n×p):

    N.sub.0 =ΣW.sub.i /X.sub.0 =M.sub.0 /X.sub.0         (5)

In the next place, at Step 4 the first maximum addable number N'_(a),1is calculated. The initial total number N₀ and the first maximum addablenumber N'_(a),1 are transferred to the register A and the register B,respectively. The method of calculating the maximum addable number is asfollows. The average weight of an already counted known number N_(k-1)of items scattering in weight with a standard deviation σ deviates by3σ/√N_(k-1) from the true average weight of the entire population at aprobability of 99.7%. In calculating, on the basis of 3σ/√N_(k-1), thenumber N'_(a),k of the items to be added to N_(k-1), the average weightof the resultant total number N_(k-1) +N'_(a),k of items would deviateby (3σ/√N_(k-1)) N'_(a),k from the true average weight of the entirepopulation, even if all the items to be added had the same weight as theaverage of the entire population. On the other hand, with theweight-scattering of the items to be added being taken intoconsideration, the resultant total average would deviate by(3σ/√N'_(a),k) N'_(a),k, even if the number N_(k-1) of items had thesame weight as the average of the entire population. In general both thedeviation (3σ/√N_(k-1)) N'_(a),k and the deviation (3σ/√N'_(a),k)N'_(a),k are encountered. Therefore, the following equation can bederived from the associative law of variance, provided that thescattering obeys the Gaussian distribution. ##EQU2## The factor 1/2 inthe parentheses on the right side is to keep a possible error not largerthan 0.5, namely to eliminate a counting error which arises in roundingoperation of the decimal figures appearing in the calculated values. Bysolving Eq. (6) with respect to N'_(a),k, with Eq. (4) introduced, thenumber N'_(a),k is given by ##EQU3## The number N'_(a),k obtained fromEq. (7) gives the abovementioned maximum addable number, namely themaximum number of items addable without generating a counting error. Thenumber N'_(a),1 is, of course, obtained from Eq. (7) by putting k=1.After the first maximum addable number N_(a),1 is obtained at Step 4, aflag 1 which shows the completion of the initial processing is set up tomake the program proceed hereafter to Step 5, where an actually addednumber N_(a),k is calculated according to the equation:

    N.sub.a,k =(M.sub.k -M.sub.k-1)/X.sub.k-1 (k=1, 2, . . . ) (8)

where M_(k) is the total weight after the k-th addition of items andX_(k) is the provisional average weight obtained from M_(k) divided byN_(k). Then it is judged whether the value of N_(a),k is equal to orsmaller or larger than the value of N'_(a),k calculated according to Eq.(7). If N_(a),k does not exceeds N'_(a),k, the program proceeds to Step6, where the contents of the register storing N_(a),k and of theregister storing the provisional average weight X_(k) are revised asfollows:

    N.sub.k ←N.sub.k-1 +N.sub.a,k                         (9)

    X.sub.k ←M.sub.k /N.sub.k                             (10)

Particularly, if N_(a),k is just equal to N'_(a),k, the display Ainforms it by several times flickering the numerical figures displayedthereon. The case of N_(a),k being larger than N'_(a),k is describedlater. Step 5 is then followed by Step 4 where the next value ofN'_(a),k is calculated again with Eq. (7). The subsequent process isrepeated through the above-described routine wherein the flag 1 is setup. In the routine, each time the items are added not in excess ofN'_(a),k both the counted total number and the maximum addable numberare increased.

On the other hand, if the items are added in excess of N'_(a),k, a flag2 which is named an over-flow flag is set up, and the excessive additionof items is informed, for instance, by displaying a predetermined blanksign instead of numerical figures on the display A. With the flag 2being set up, the program flow is directed to Step 7, where the numberN_(a),k -N'_(a),k of items to be removed from the scale is calculatedand displayed on the display B. The flag 2 is set down if a relationN_(a),k ≦N'_(a),k is achieved by removing a certain number of items.

The method of calculating the maximum addable number N'_(a),k may besubstituted by another one. In case, for instance, the number of itemsfirst sampled for estimating the weight-scattering of the population issmall, the concept of the t-distribution may be introduced to increasethe accuracy of the measurement. A constant t in the t-distribution isgiven by ##EQU4## where X is a calculated average, μ the true average ofthe population, σ the standard deviation and N the number of items. Thet-distribution is described in a standard textbook of statistics. On theother hand the degree of freedom (p-1) is determined from the number pof sampling, and the constant t which gives a probability 95% at p=3 isshown to be 4.303 in the table of t-distribution. It is shown from Eq.(11) that the true average value μ remains within ##EQU5## at theprobability of 95%. For convenience of calculation, putting ##EQU6## themaximum addable number N'_(b) free from a counting error is obtainedfrom

    N'.sub.b =0.4(X-K)/K                                       (14)

With respect to this method of calculation a flow chart is not shownherein.

Another embodiment of the present invention is described in thefollowing. In this embodiment the coefficient of variation C_(v) (or thestandard deviation σ) is already known, and the maximum addable numberN'_(a),k is calculated beforehand with C_(v) used as a paremeter, andstored in the memory in the form of a table or a function curve.

FIG. 3 shows a flow-chart in which a scale operator inputs C_(v) throughthe key board 5 and operates a setting completion key 53 on the keyboard 5. With the setting completion key pushed, a flag A and a flag Bare set up. As a result the program proceeds to Step 8, where an averageX is calculated. In this embodiment the register stores N=5, because thenumber of items to be loaded in the first place is determined to be 5.After a calculation of X, the flag B is set down and Step 8 is followedby Step 9, where a maximum addable number N'_(a),k is read out from thefunction table stored previously in the memory. This table shows themaximum number N'_(a),k addable to the already known counted numbersN_(k-1), with a coefficients of variation C_(v) used as a parameter.

    ______________________________________                                        N'.sub.a,k                                                                    C.sub.v                                                                       N.sub.k-1                                                                             0.002   0.003    0.005                                                                              0.01    0.02 0.03                               ______________________________________                                         5 ˜ 15                                                                         180     120       70  35      16   10                                 16 ˜ 50                                                                         300     200      120  56      26   15                                  51 ˜ 100                                                                       550     360      210  94      40   21                                 101 ˜ 300                                                                       760     500      280  120     46   24                                 301 up  1300    840      450  170     58   26                                 ______________________________________                                    

With the flag B and a flag C set down, N_(a),k N'_(a),k is judged. Theprocess of judgement is similar to that employed in the flow chart shownin FIG. 2, so the description is left out.

What is claimed is:
 1. An electronic counting scale comprising aweighing tray to be loaded with items whose number is to be counted, aweight measuring means for measuring a gravitational force acting onsaid items loaded on said tray and for outputting a digital weight valuecorresponding to said gravitational force, a central processing unitwhich includes an arithmetic organ for processing said digital weightvalue according to a predetermined program, a memory for storing variouscalculating formulae, various calculated values and said predeterminedprogram, said various calculating formulae containing a maximum numbercalculating formula which gives, in consideration of the weightfluctuations of the items to be counted, a maximum addable numberrounded to the nearest whole number for fractions equal to or over 0.5without giving a counting error, a number displaying means fordisplaying the number of said items calculated by said arithmetic organ,and an informing means for informing whether an unknown number of itemsadded to an already counted known number of items is equal to or exceedssaid maximum addable number calculated according to said maximum addablenumber calculating formula.
 2. An electronic counting scale defined inclaim 1, wherein said informing means eliminates the display on saidnumber displaying means, if said unknown number of items added exceedssaid maximum addable maximum number.
 3. An electronic counting scaledefined in claim 1, wherein said informing means flickers the display onsaid number displaying means, if said unknown number of items addedcoincides with said maximum addable number.
 4. An electronic countingscale defined in claim 1, wherein a numerical figure displayer isprovided which displays said maximum addable number.
 5. An electroniccounting scale defined in claim 1, wherein a numerical figure displayeris provided which displays the calculated number of actually addeditems.
 6. An electronic counting scale defined in claim 1, wherein anumerical figure displayer is provided which displays the difference innumber between said maximum addable number and the calculated number ofactually added items if said informing means informs an addition ofitems in excess of said maximum addable number.
 7. An electroniccounting scale defined in claim 1, wherein if a calculated number ofactually added items exceeds said maximum addable number, the display onsaid number displaying means is eliminated and then substituted by thedifference in number between said calculated number of actually addeditems and said maximum addable number.
 8. An electronic counting scaledefined in claim 1, wherein whenever the number of actually added itemsis judged to exceed said maximum addable number, the following processof calculation is prohibited.
 9. An electronic counting scale defined inclaim 1, wherein said arithmetic organ mentioned in claim 1 calculatessaid maximum addable number N'_(a),k according to the equation ##EQU7##where N_(k-1) is a known counted number and C_(v) is the coefficient ofvariation.
 10. An electronic counting scale defined in claim 1, whereinsaid arithmetic organ calculates said maximum addable number N'_(b)according to the following equation derived from a constant t in thet-distribution with a degree of freedom (p-1)

    N'.sub.b =α(X-K)/X

where X is the average obtained from the weight measurements of a knownnumber p of the samples, each of which consists of a known number N ofitems, σ is the standard deviation, α is a constant regarding to therounding operation on the numerical figure, and K=±tσ/√N.